Rattled, Labor had jumped at shadows. Twenty billion of its total shouldn't have been there and much of the rest was guesswork based on figures the Coalition hadn't yet provided, or had provided but Labor chose not to believe.

There's never any point in claiming the other side has a black hole early in the campaign, and hasn't been for more than a decade.

Here's how it has worked since the start of the century: 1. Each side makes promises. 2. Each side publishes an estimate of the cost of each promise over the next four years. 3. At the end of the campaign, when all the promises are public, each side produces a tally of what it proposes to spend (which it has usually proudly trumpeted) and what it proposes to save (about which it has usually been more quiet ).

And guess what? The proposed savings always slightly exceed the proposed spending, leaving the budget slightly better off over four years.

That's not to say that things will turn out that way. Last time the Coalition's costings pointed to a slight $1.5 billion-a-year improvement in the budget deficit. Instead, the projected deficit blew out from $7 billion to $37 billion. That's partly because company tax revenues didn't recover in the way that was expected, and partly because the Coalition never got to implement many of its policies. One was axing Labor's low-income super contribution. It was held up in the Senate for two years and then withdrawn in this year's budget because it was heartless.

But the tally of costings released at the end of the campaign almost always does add up and always puts the budget slightly ahead. There's never a black hole.

Which makes Tuesday's attempt by the Coalition's to find a hole in Labor's program a triumph of hope over experience. Where was Joe Hockey when they needed him? Neither the Coalition's Finance spokesman Mathias Cormann nor its Treasury spokesmen Scott Morrison were in their jobs back in 2013 when Labor self-immolated over its claim of a $70 billion black hole. So they cooked up their own, worth $67 billion.

Much of it was fiction. A whopping $19.27 billion, a quarter of the total, was a misreading of Labor's foreign aid commitment. Labor has promised to boost spending by less than $1 billion over the next four years. Cormann and Morrison penciled in $19.27 billion on the basis of an ill-defined commitment to restore cuts Tanya Plibersek made a year ago in a Newcastle radio interview. On Sunday she released the actual policy, but Cormann and Morrison didn't bother to update their spreadsheet.

They claimed Labor would spend $6.73 billion lifting compulsory super contributions to 12 per cent of salary even though the specifics of the promise weren't announced; specifics such as how quickly Labor would phase in the increase and whether it believed it could afford to do it in the next four years at all. The "commitment" came from an interview Bill Shorten did on RN Drive in which he talked about what he would like to do "over time, over the long run".

The mistakes say much about the helplessness of government staffers when they are without the support of the bureaucracy.

The mistakes, and there were many more, say much about the helplessness of government staffers when they are without the support of the bureaucracy. They would be well advised to install a pop-up on their screens reading: "What would treasury do".

But even were there no mistakes, the exercise of looking for a black hole would be pointless. It isn't until the end of the campaign when all the policies and the means to fund them are on the table that a spendometer make sense. And by then it's too late. Last time the Coalition released its tally on the Thursday, 1½ days before the vote.

I can already tell you what Labor's tally will say. Like the Coalition's last time it will show a slight improvement in the budget's position. And like the Coalition's it'll get a tick from the Parliamentary Budget Office when it issues the required report 30 days after the vote. Politicians are good at costing their own promises, bad at costing those of the other side.

If the black hole hunters were serious about bringing us the truth, they would change the law to require the PBO to publish a running total of promises, and also require it to make public the methods by which it arrives at the costings politicians quote.

In the meantime it would be nice if they shut up at the debate between Treasurer and shadow treasurer on Friday. The purpose of what they are proposing is much more important than whether the other side thinks the numbers add up.